Add helpers to setup and teardown fbdev emulation.
Signed-off-by: NNoralf Trønnes <noralf@tronnes.org>
Reviewed-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20171215175119.36181-3-noralf@tronnes.org